System and method for avoiding, reversing, and managing neurological accommodation to electrical stimulation

ABSTRACT

A method of operating a neurostimulation device comprises varying a first stimulation parameter under user control while fixing a second stimulation parameter, generating a plurality of stimulation parameter sets from the varied first stimulation parameter and the fixed second stimulation parameter, outputting a pulsed electrical waveform from the neurostimulation device between electrodes in accordance with the stimulation parameter sets, such that a therapeutic effect is achieved while allowing neural tissue to undergo neurological accommodation, changing the second stimulation parameter, varying the first stimulation parameter under user control while fixing the second changed stimulation parameter, generating another plurality of stimulation parameter sets from the varied first stimulation parameter and the fixed changed second stimulation parameter, and outputting the pulsed electrical waveform from the neurostimulation device between the electrodes in accordance with the other stimulation parameter sets to maintain the therapeutic effect while the neural tissue is neurologically accommodated.

RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 12/509,340, filed Jul. 24, 2009, which claims the benefit under35 U.S.C. §119 to U.S. provisional patent application Ser. No.61/083,490, filed Jul. 24, 2008. The foregoing applications are herebyincorporated by reference in the present application in theirentireties.

FIELD OF THE INVENTION

The present invention relates to tissue stimulation systems, and moreparticularly, to a system and method for programming an implantabletissue stimulator.

BACKGROUND OF THE INVENTION

Spinal cord stimulation (SCS) is a well-accepted clinical method forreducing pain in certain populations of patients. Spinal cord stimulatorand other implantable tissue stimulator systems come in two generaltypes: radio-frequency (RF)-controlled and fully implanted.

The type commonly referred to as an “RF” system includes an external RFtransmitter inductively coupled via an electromagnetic link to animplanted receiver-stimulator connected to one or more leads with one ormore electrodes for stimulating tissue. The power source, e.g., abattery, for powering the implanted receiver, as well as controlcircuitry to command the receiver-stimulator, is contained in the RFtransmitter—a hand-held sized device typically worn on the patient'sbelt or carried in a pocket. Data/power signals are transcutaneouslycoupled from a cable-connected transmission coil connected to the RFtransmitter and placed over the implanted receiver-stimulator. Theimplanted receiver-stimulator receives the signal and generates thestimulation.

In contrast, the fully implanted type of stimulating system contains thecontrol circuitry, as well as a power supply, e.g., a battery, allwithin an implantable pulse generator (IPG), so that once programmed andturned on, the IPG can operate independently of external hardware. TheIPG is turned on and off and programmed to generate the desiredstimulation pulses from an external portable programming device usingtranscutaneous electromagnetic or RF links.

In both the RF-controlled or fully implanted systems, the electrodeleads are implanted in the epidural space, or alternatively near thedura of the spinal cord. Individual wires within one or more electrodeleads connect with each electrode on the lead. The electrode leads exitthe spinal column and, when necessary, attach to one or more electrodelead extensions. The electrode leads or extensions are typicallytunneled within the subcutaneous tissue along the torso of the patientto a subcutaneous pocket where the receiver-stimulator or IPG isimplanted. The RF transmitter or IPG can then be operated to generateelectrical pulses that are delivered, through the electrodes, to thetargeted tissue, and in particular, the dorsal column fibers and dorsalroot fibers within the spinal cord. The stimulation creates thesensation known as paresthesia, which can be characterized as analternative sensation that replaces the pain signals sensed by thepatient.

Individual electrode contacts (the “electrodes”) are arranged in adesired pattern and spacing in order to create an electrode array. Thecombination of electrodes used to deliver electrical pulses to thetargeted tissue constitutes an electrode combination, with theelectrodes capable of being selectively programmed to act as anodes(positive), cathodes (negative), or left off (zero). In other words, anelectrode combination represents the polarity being positive, negative,or zero. Other parameters that may be controlled or varied in SCSinclude electrical pulse parameters, which may define the pulseamplitude (measured in milliamps or volts depending on whether constantcurrent or constant voltage is supplied to the electrodes), pulseduration (measured in microseconds), pulse rate (measured in pulses persecond), pulse shape, and burst rate (measured as the stimulation onduration per unit time). Each electrode combination, along with theelectrical pulse parameters, can be referred to as a “stimulationparameter set.”

With some SCS systems, and in particular, SCS systems with independentlycontrolled current or voltage sources, the distribution of the currentto the electrodes (including the case of the receiver-stimulator or IPG,which may act as an electrode) may be varied such that the current issupplied via numerous different electrode configurations. In differentconfigurations, the electrodes may provide current (or voltage) indifferent relative percentages of positive and negative current (orvoltage) to create different electrode configuration, and in particular,fractionalized electrode configurations.

As briefly discussed above, an external control device, such as an RFcontroller or portable programming device, can be used to instruct thereceiver-stimulator or IPG to generate electrical stimulation pulses inaccordance with the selected stimulation parameters. Typically, thestimulation parameters programmed into the external device, itself, canbe adjusted by manipulating controls on the external device itself tomodify the electrical stimulation provided by the SCS system to thepatient. However, the number of electrodes available, combined with theability to generate a variety of complex stimulation pulses, presents ahuge selection of stimulation parameter sets to the clinician orpatient.

To facilitate such selection, the clinician generally programs theexternal control device, and if applicable the IPG, through acomputerized programming system. This programming system can be aself-contained hardware/software system, or can be defined predominantlyby software running on a standard personal computer (PC). The PC orcustom hardware may actively control the characteristics of theelectrical stimulation generated by the receiver-stimulator or IPG toallow the optimum stimulation parameters to be determined based onpatient feedback and to subsequently program the RF transmitter orportable programming device with the optimum stimulation parameters. Thecomputerized programming system may be operated by a clinician attendingthe patient in several scenarios.

For example, in order to achieve an effective result from SCS, the leador leads must be placed in a location, such that the electricalstimulation will cause paresthesia. The paresthesia induced by thestimulation and perceived by the patient should be located inapproximately the same place in the patient's body as the pain that isthe target of treatment. If a lead is not correctly positioned, it ispossible that the patient will receive little or no benefit from animplanted SCS system. Thus, correct lead placement can mean thedifference between effective and ineffective pain therapy. Whenelectrical leads are implanted within the patient, the computerizedprogramming system, in the context of an operating room (OR) mappingprocedure, may be used to instruct the RF transmitter or IPG to applyelectrical stimulation to test placement of the leads and/or electrodes,thereby assuring that the leads and/or electrodes are implanted ineffective locations within the patient.

Once the leads are correctly positioned, a fitting procedure, which maybe referred to as a navigation session, may be performed using thecomputerized programming system to program the external control device,and if applicable the IPG, with a set of stimulation parameters thatbest addresses the painful site. Thus, the navigation session may beused to pinpoint the stimulation region or areas correlating to thepain. Such programming ability is particularly advantageous afterimplantation should the leads gradually or unexpectedly move, therebyrelocating the paresthesia away from the pain site. By reprogramming theexternal control device, the stimulation region can often be moved backto the effective pain site without having to reoperate on the patient inorder to reposition the lead and its electrode array.

Even when using a computerized programming system, programming orreprogramming the external control device or IPG may be a difficulttask. Oftentimes, a clinician may identify a stimulation parameter setwhere a patient is obtaining great paresthesia, but when the cliniciansubsequently returns to this stimulation parameter set, even within thesame programming session, the patient may no longer receive the sameparesthesia. In some cases, the patient may not feel any paresthesia atall when the clinician returns to this stimulation parameter set.

Candidate reasons for the change in paresthesia over time are neurologicphenomena, such as accommodation, adaptation, and habituation, whichentail a diminished neural response over time when there existscontinuous input (in this case, electrical stimulation) due to cellularand synaptic mechanisms. For the purposes of this specification, we willuse the term “accommodation” to generally refer to any mechanism thatdiminishes neural response due to continuous input. Currently-usedmethods to avoid accommodation include a 1-hour rest interval to avoidaccommodation of nerve fibers (see Benedetti, Fabrizio M D, et al;Control of Postoperative Pain by Transcutaneous Electrical NerveStimulation After Thoracic Operations. Ann Thorac Surg 1997; 63:773-776). However, this is an unrealistic solution as it would more thandouble the time needed for a programming session. Increased programmingtime leads to higher workloads for the clinicians and increased costs.Furthermore, once neurological accommodation has occurred, there arecurrently no techniques to reverse or otherwise manage theaccommodation.

There, thus, remains a need for an improved method and system thatavoids, reverses, or otherwise manages neurological accommodation duringthe programming of neurostimulation devices.

SUMMARY OF THE INVENTION

The present inventions are directed to methods and programmers foravoiding, reversing, or otherwise managing neurological accommodation;

In accordance with a first aspect of the present inventions, a method ofprogramming a neurostimulation device is provided. The method comprisesvarying a first stimulation parameter (e.g., an electrode combination ora fractionalized electrode combination) under user control. If the firststimulation parameter is a fractionalized electrode combination, it canbe varied by gradually shifting current between anodic electrodes orgradually shifting current between cathodic electrodes.

The method further comprises automatically varying a second stimulationparameter as the first stimulation parameter is varied under usercontrol. In one method, the second stimulation parameter ispseudo-randomly or randomly varied. The second stimulation parameter maybe, e.g., an electrode combination or an electrical pulse parameter,such as a pulse amplitude, pulse width, a pulse shape, or burst rate. Ifthe second stimulation parameter is a pulse amplitude, it can be variedby both increasing and decreasing the amplitude of the pulses. If boththe pulse amplitude and pulse width are varied, they can be inverselyvaried relative to each other, e.g., such that the pulsed electricalwaveform is maintained within a predetermined range of astrength-duration curve for the neural tissue.

The method further comprises generating a plurality of stimulationparameter sets from the varied first and second stimulation parameters,and outputting a pulsed electrical waveform from the neurostimulationdevice between a plurality of electrodes in accordance with theplurality of stimulation parameter sets, such that neural tissue (e.g.,spinal cord tissue) is stimulated without undergoing neurologicalaccommodation that would otherwise occur if the second stimulationparameter were not varied. The method further comprises programming theneurostimulation device with a new set of stimulation parameters basedon a result of the neural tissue stimulation.

In accordance with a second aspect of the present inventions, aprogrammer for a neurostimulation device is provided. The programmercomprises a user interface capable of receiving an input from a user,and a processor configured for varying a first stimulation parameter inresponse to the user input, automatically varying a second stimulationparameter as the first stimulation parameter is varied in response tothe user input, generating a plurality of stimulation parameter setsfrom the varied first and second stimulation parameters, and programmingthe neurostimulation device with a new set of stimulation parameters.

The processor may vary the first and second stimulation parameters inthe manner described above. The user interface may comprise an actuator,in which case, the processor may be configured for generating theplurality of stimulation parameter sets in response to actuation of theactuator. The programmer further comprises output circuitry configuredfor transmitting the plurality of stimulation parameter sets and the newstimulation parameter set to the neurostimulation device. The outputcircuitry may be telemetry circuitry configured for wirelesslytransmitting the plurality of stimulation parameter sets and the newstimulation parameter set to the neurostimulation device.

In accordance with a third aspect of the present inventions, a method ofoperating a neurostimulation device is provided. The method comprisesoutputting a pulsed electrical waveform from the neurostimulation devicebetween a plurality of electrodes while at least one of the electrodeshas a first polarity, thereby stimulating neural tissue adjacent the atleast one electrode. In one method, the pulsed electrical waveform isoutput between the electrodes in accordance with a set of stimulationparameters, in which case, the method further comprises varying one ormore of the stimulation parameters under user control as the pulsedelectrical waveform is output between the electrodes while theelectrode(s) has the first polarity.

The method further comprises allowing the neural tissue to undergoneurological accommodation in response to the electrical energy outputbetween the electrodes, switching the electrode(s) from the firstpolarity to a second polarity (which may be automatically initiated),and outputting the pulsed electrical waveform from the neurostimulationdevice between the electrodes while the electrode(s) has the secondpolarity, thereby hyperpolarizing the neural tissue to reverse theneurological accommodation.

The method further comprises switching the electrode(s) from the secondpolarity to the first polarity (which may be automatically initiated),and outputting the pulsed electrical waveform from the neurostimulationdevice between the electrodes while the electrode(s) has the firstpolarity, thereby stimulating the previously hyperpolarized neuraltissue. In one method, each of the electrode(s) is a cathode when in thefirst polarity, and is an anode when in the second polarity. In anothermethod, the pulsed electrical waveform output has a first amplitude whenthe electrode(s) has the first polarity, and the pulsed electricalwaveform output has a second lesser amplitude when the electrode(s) hasthe second polarity. For example, the second amplitude may be equal to athird or less of the first amplitude. The method may optionally compriseprogramming the neurostimulation device with a new set of stimulationparameters based on a result of the neural tissue stimulation.

In accordance with a fourth aspect of the present invention anothermethod of operating a neurostimulation device is provided. The methodcomprises varying a first stimulation parameter (e.g., an electrodecombination or a fractionalized electrode combination) under usercontrol while fixing a second stimulation parameter (e.g., a pulse rateor pulse width). If the first stimulation parameter is a fractionalizedelectrode combination, it can be varied by gradually shifting currentbetween anodic electrodes or gradually shifting current between cathodicelectrodes.

The method further comprises generating a plurality of stimulationparameter sets from the varied first stimulation parameter and the fixedsecond stimulation parameter, and outputting a pulsed electricalwaveform from the neurostimulation device between a plurality ofelectrodes in accordance with the plurality of stimulation parametersets, such that a therapeutic effect (e.g., pain relief) is achievedwhile allowing neural tissue (e.g., spinal cord tissue) to undergoneurological accommodation.

The method further comprises changing the second stimulation parameter(which may be automatically initiated), and varying the firststimulation parameter under user control while fixing the second changedstimulation parameter.

In one method, the second stimulation parameter is changed in accordancewith a predetermined curve. In this case, the predetermined curve may bebased on data collected from patients that have undergone neurologicalaccommodation.

In another method, a reference set of stimulation parameters isgenerated from a first reference stimulation parameter of the same typeas the first stimulation parameter, and a second stimulation parameterof the same type as the second stimulation parameter. Prior to allowingthe neural tissue to undergo neurological accommodation, the pulsedelectrical waveform is outputted from the neurostimulation devicebetween the electrodes in accordance with the reference stimulationparameter set, thereby stimulating the neural tissue to provide areference therapeutic effect. After allowing the neural tissue toundergo neurological accommodation, the pulsed electrical waveform isoutputted from the neurostimulation device between the electrodes inaccordance with the reference stimulation parameter set, therebyproviding an effect different from the reference therapeutic effect, andvarying the second reference stimulation parameter until the effectmatches the reference therapeutic effect. The varied second referencestimulation parameter is then used as the changed second stimulationparameter.

The method further comprises generating another plurality of stimulationparameter sets from the varied first stimulation parameter and the fixedchanged second stimulation parameter, outputting the pulsed electricalwaveform from the neurostimulation device between the plurality ofelectrodes in accordance with the other plurality of stimulationparameter sets to maintain the therapeutic effect while the neuraltissue is neurologically accommodated. The method may optionallycomprise programming the neurostimulation device with a new set ofstimulation parameters based on a result of the therapeutic effect.

In accordance with a fifth aspect of the present invention, stillanother method of operating a neurostimulation device is provided. Themethod comprises outputting a pulsed electrical waveform from theneurostimulation device between a plurality of electrodes in accordancewith a specified pulse amplitude and a specified pulse width.

The method further comprises maintaining the pulsed electrical waveformbetween a first strength-duration curve for relatively large fibers ofneural tissue (e.g., spinal cord tissue) and a second strength-durationcurve for relatively small fibers of the neural tissue, whereby therelatively large fibers are stimulated and the relatively small fibersare not stimulated.

The method further comprises allowing the relatively large fibers of theneural tissue to neurologically accommodation when the pulsed electricalwaveform is between the first and second strength-duration curves, andincreasing one or both of the specified amplitude and the specifiedpulse width, such that the pulsed electrical waveform is on or above thesecond strength-duration curve, whereby the relatively small fibers arestimulated.

In one method, the specified amplitude and the specified pulse width areautomatically increased. In another method, one or both of the specifiedamplitude and the specified pulse width is increased at a predeterminedperiod of time after the pulsed electrical waveform is initially outputby the neurostimulation device. The method may optionally compriseprogramming the neurostimulation device with a new set of stimulationparameters based on a result of the neural stimulation.

The method may further comprise varying a stimulation parameter (e.g.,an electrode combination or a fractionalized electrode combination)under user control. If the stimulation parameter is a fractionalizedelectrode combination, it can be varied by gradually shifting currentbetween the anodic electrodes or gradually shifting current between thecathodic electrodes.

In accordance with a sixth aspect of the present invention, yet anothermethod of programming a neurostimulation device is provided. The methodcomprises initially outputting a pulsed electrical waveform from theneurostimulation device between a plurality of electrodes, such thatneural tissue (e.g., spinal cord tissue) of a patient is stimulated andundergoes neurological accommodation. In one method, the pulsedelectrical waveform is initially output with the highest pulse amplitudetolerable for the patient. The method further comprises decreasing apulse amplitude of the pulsed electrical waveform, and generating aplurality of stimulation parameter sets having the decreased amplitude.

The method further comprises outputting the pulsed electrical waveformwith the decreased pulse amplitude in accordance with the stimulationparameter sets, such that the neural tissue is stimulated and remainsneurologically accommodated, and programming the neurostimulation devicewith a new set of stimulation parameters based on a result of the neuraltissue stimulation.

The method may further comprise varying a stimulation parameter (e.g.,an electrode combination or a fractionalized electrode combination)under user control, in which case, the plurality of stimulationparameter sets are generated from the varied stimulation parameter. Ifthe stimulation parameter is a fractionalized electrode combination, itcan be varied by gradually shifting current between anodic ones of theelectrodes or gradually shifting current between cathodic ones of theelectrodes.

Other and further aspects and features of the invention will be evidentfrom reading the following detailed description of the preferredembodiments, which are intended to illustrate, not limit, the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the design and utility of preferred embodimentsof the present invention, in which similar elements are referred to bycommon reference numerals. In order to better appreciate how theabove-recited and other advantages and objects of the present inventionsare obtained, a more particular description of the present inventionsbriefly described above will be rendered by reference to specificembodiments thereof, which are illustrated in the accompanying drawings.Understanding that these drawings depict only typical embodiments of theinvention and are not therefore to be considered limiting of its scope,the invention will be described and explained with additionalspecificity and detail through the use of the accompanying drawings inwhich:

FIG. 1 is perspective view of one embodiment of a SCS system arranged inaccordance with the present inventions;

FIG. 2 is a side view of an implantable pulse generator and a pair ofstimulation leads that can be used in the SCS system of FIG. 1;

FIG. 3 is a plan view of the SCS system of FIG. 1 in use with a patient;

FIG. 4 is a block diagram of the internal componentry of the IPG of FIG.2;

FIG. 5 is a plan view of a remote control that can be used in the SCSsystem of FIG. 1;

FIG. 6 is a block diagram of the internal componentry of the remotecontrol of FIG. 5;

FIG. 7 is a block diagram of the components of a computerizedprogramming system that can be used in the SCS system of FIG. 1;

FIG. 8 is an exemplary mono-phasic pulsed electrical waveform that canbe output by the IPG of FIG. 2 to prevent neurological accommodation ofspinal cord tissue;

FIG. 9 is an exemplary bi-phasic pulsed electrical waveform that can beoutput by the IPG of FIG. 2 to prevent neurological accommodation ofspinal cord tissue;

FIG. 10 is another exemplary mono-phasic pulsed electrical waveform thatcan be output by the IPG of FIG. 2 to prevent neurological accommodationof spinal cord tissue;

FIG. 11 is an exemplary plot of a strength-duration curve having a usagerange in which the mono-phasic pulsed electrical waveform of FIG. 10 ismaintained;

FIG. 12 is still another exemplary mono-phasic pulsed electricalwaveform that can be output by the IPG of FIG. 2 to prevent neurologicalaccommodation of spinal cord tissue;

FIG. 13 is a predetermined pulse rate or pulse width curve that can beused to output a pulse electrical waveform from the IPG of FIG. 2 tomanage neurological accommodation of the spinal cord tissue;

FIG. 14 is a flow diagram of a method used to manage neurologicalaccommodation of the spinal cord tissue; and

FIG. 15 is an exemplary plot of two strength-duration curves forrespective small diameter fibers and large diameter fibers that can beused to manage neurological accommodation of the spinal cord tissue.

DETAILED DESCRIPTION OF THE EMBODIMENTS

At the outset, it is noted that the present invention may be used withan implantable pulse generator (IPG), radio frequency (RF) transmitter,or similar electrical stimulator, that may be used as a component ofnumerous different types of stimulation systems. The description thatfollows relates to a spinal cord stimulation (SCS) system. However, itis to be understood that the while the invention lends itself well toapplications in SCS, the invention, in its broadest aspects, may not beso limited. Rather, the invention may be used with any type ofimplantable electrical circuitry used to stimulate tissue. For example,the present invention may be used as part of a pacemaker, adefibrillator, a cochlear stimulator, a retinal stimulator, a stimulatorconfigured to produce coordinated limb movement, a cortical stimulator,a deep brain stimulator, peripheral nerve stimulator, microstimulator,or in any other neural stimulator configured to treat urinaryincontinence, sleep apnea, shoulder sublaxation, headache, etc.

Turning first to FIG. 1, an exemplary SCS system 10 generally includesone or more (in this case, two) implantable stimulation leads 12, animplantable pulse generator (IPG) 14, an external remote controller RC16, a clinician's programmer (CP) 18, an external trial stimulator (ETS)20, and an external charger 22.

The IPG 14 is physically connected via one or more percutaneous leadextensions 24 to the stimulation leads 12, which carry a plurality ofelectrodes 26 arranged in an array. In the illustrated embodiment, thestimulation leads 12 are percutaneous leads, and to this end, theelectrodes 26 are arranged in-line along the stimulation leads 12. Inalternative embodiments, the electrodes 26 may be arranged in atwo-dimensional pattern on a single paddle lead. As will be described infurther detail below, the IPG 14 includes pulse generation circuitrythat delivers electrical stimulation energy in the form of a pulsedelectrical waveform (i.e., a temporal series of electrical pulses) tothe electrode array 26 in accordance with a set of stimulationparameters.

The ETS 20 may also be physically connected via the percutaneous leadextensions 28 and external cable 30 to the stimulation leads 12. The ETS20, which has similar pulse generation circuitry as the IPG 14, alsodelivers electrical stimulation energy in the form of a pulse electricalwaveform to the electrode array 26 in accordance with a set ofstimulation parameters. The major difference between the ETS 20 and theIPG 14 is that the ETS 20 is a non-implantable device that is used on atrial basis after the stimulation leads 12 have been implanted and priorto implantation of the IPG 14, to test the responsiveness of thestimulation that is to be provided. Further details of an exemplary ETSare described in U.S. Pat. No. 6,895,280, which is expresslyincorporated herein by reference.

The RC 16 may be used to telemetrically control the ETS 20 via abi-directional RF communications link 32. Once the IPG 14 andstimulation leads 12 are implanted, the RC 16 may be used totelemetrically control the IPG 14 via a bi-directional RF communicationslink 34. Such control allows the IPG 14 to be turned on or off and to beprogrammed with different stimulation parameter sets. The IPG 14 mayalso be operated to modify the programmed stimulation parameters toactively control the characteristics of the electrical stimulationenergy output by the IPG 14. As will be described in further detailbelow, the CP 18 provides clinician detailed stimulation parameters forprogramming the IPG 14 and ETS 20 in the operating room and in follow-upsessions.

The CP 18 may perform this function by indirectly communicating with theIPG 14 or ETS 20, through the RC 16, via an IR communications link 36.Alternatively, the CP 18 may directly communicate with the IPG 14 or ETS20 via an RF communications link (not shown). The clinician detailedstimulation parameters provided by the CP 18 are also used to programthe RC 16, so that the stimulation parameters can be subsequentlymodified by operation of the RC 16 in a stand-alone mode (i.e., withoutthe assistance of the CP 18).

The external charger 22 is a portable device used to transcutaneouslycharge the IPG 14 via an inductive link 38. For purposes of brevity, thedetails of the external charger 22 will not be described herein. Detailsof exemplary embodiments of external chargers are disclosed in U.S. Pat.No. 6,895,280, which has been previously incorporated herein byreference. Once the IPG 14 has been programmed, and its power source hasbeen charged by the external charger 22 or otherwise replenished, theIPG 14 may function as programmed without the RC 16 or CP 18 beingpresent.

Referring now to FIG. 2, the external features of the stimulation leads12 and the IPG 14 will be briefly described. One of the stimulationleads 12 has eight electrodes 26 (labeled E1-E8), and the otherstimulation lead 12 has eight electrodes 26 (labeled E9-E16). The actualnumber and shape of leads and electrodes will, of course, vary accordingto the intended application. The IPG 14 comprises an outer case 40 forhousing the electronic and other components (described in further detailbelow), and a connector 42 to which the proximal ends of the stimulationleads 12 mate in a manner that electrically couples the electrodes 26 tothe internal electronics (described in further detail below) within theouter case 40. The outer case 40 is composed of an electricallyconductive, biocompatible material, such as titanium, and forms ahermetically sealed compartment wherein the internal electronics areprotected from the body tissue and fluids. In some cases, the outer case40 may serve as an electrode.

The IPG 14 includes a battery and pulse generation circuitry thatdelivers the electrical stimulation energy in the form of a pulsedelectrical waveform to the electrode array 26 in accordance with a setof stimulation parameters programmed into the IPG 14. Such stimulationparameters may comprise electrode combinations, which define theelectrodes that are activated as anodes (positive), cathodes (negative),and turned off (zero), percentage of stimulation energy assigned to eachelectrode (fractionalized electrode configurations), and electricalpulse parameters, which define the pulse amplitude (measured inmilliamps or volts depending on whether the IPG 14 supplies constantcurrent or constant voltage to the electrode array 26), pulse width(measured in microseconds), and pulse rate (measured in pulses persecond).

Electrical stimulation will occur between two (or more) activatedelectrodes, one of which may be the IPG case. Simulation energy may betransmitted to the tissue in a monopolar or multipolar (e.g., bipolar,tripolar, etc.) fashion. Monopolar stimulation occurs when a selectedone of the lead electrodes 26 is activated along with the case of theIPG 14, so that stimulation energy is transmitted between the selectedelectrode 26 and case. Bipolar stimulation occurs when two of the leadelectrodes 26 are activated as anode and cathode, so that stimulationenergy is transmitted between the selected electrodes 26. For example,electrode E3 on the first lead 12 may be activated as an anode at thesame time that electrode E11 on the second lead 12 is activated as acathode. Tripolar stimulation occurs when three of the lead electrodes26 are activated, two as anodes and the remaining one as a cathode, ortwo as cathodes and the remaining one as an anode. For example,electrodes E4 and E5 on the first lead 12 may be activated as anodes atthe same time that electrode E12 on the second lead 12 is activated as acathode.

The stimulation energy may be delivered between electrodes as monophasicelectrical energy or multiphasic electrical energy. Monophasicelectrical energy includes a series of pulses that are either allpositive (anodic) or all negative (cathodic). Multiphasic electricalenergy includes a series of pulses that alternate between positive andnegative. For example, multiphasic electrical energy may include aseries of biphasic pulses, with each biphasic pulse including a cathodic(negative) stimulation pulse and an anodic (positive) recharge pulsethat is generated after the stimulation pulse to prevent direct currentcharge transfer through the tissue, thereby avoiding electrodedegradation and cell trauma. That is, charge is conveyed through theelectrode-tissue interface via current at an electrode during astimulation period (the length of the stimulation pulse), and thenpulled back off the electrode-tissue interface via an oppositelypolarized current at the same electrode during a recharge period (thelength of the recharge pulse).

As shown in FIG. 3, the electrode leads 12 are implanted within thespinal column 52 of a patient 50. The preferred placement of theelectrode leads 12 is adjacent, i.e., resting upon near, or upon thedura, adjacent to the spinal cord area to be stimulated. Due to the lackof space near the location where the electrode leads 12 exit the spinalcolumn 52, the IPG 14 is generally implanted in a surgically-made pocketeither in the abdomen or above the buttocks. The IPG 14 may, of course,also be implanted in other locations of the patient's body. The leadextension 24 facilitates locating the IPG 14 away from the exit point ofthe electrode leads 12. As there shown, the CP 18 communicates with theIPG 14 via the RC 16.

Turning next to FIG. 4, the main internal components of the IPG 14 willnow be described. The IPG 14 includes stimulation output circuitry 60configured for generating electrical stimulation energy in accordancewith a defined pulsed waveform having a specified pulse amplitude, pulserate, pulse width, and pulse shape under control of control logic 62over data bus 64. Control of the pulse rate and pulse width of theelectrical waveform is facilitated by timer logic circuitry 66, whichmay have a suitable resolution, e.g., 10 μs. The stimulation energygenerated by the stimulation output circuitry 60 is output viacapacitors C1-C16 to electrical terminals 68 corresponding to electrodesE1-E16.

The analog output circuitry 60 may either comprise independentlycontrolled current sources for providing stimulation pulses of aspecified and known amperage to or from the electrical terminals 68, orindependently controlled voltage sources for providing stimulationpulses of a specified and known voltage at the electrical terminals 68or to multiplexed current or voltage sources that are then connected tothe electrical terminals 68. The operation of this analog outputcircuitry, including alternative embodiments of suitable outputcircuitry for performing the same function of generating stimulationpulses of a prescribed amplitude and width, is described more fully inU.S. Pat. Nos. 6,516,227 and 6,993,384, which are expressly incorporatedherein by reference. The analog output circuitry 60 may also comprisepulse shaping circuitry (not shown) capable of shaping the pulses (e.g.,a square pulse, an exponential pulse, a logarithmic pulse, a rampedpulse, a trapezoidal pulse, etc.). Further details discussing pulseshaping circuitry and the different pulse shapes that can be generatedare disclosed in U.S. Patent Application Ser. No. 60/951,177, entitled“Use of Stimulation Pulse Shape to Control Neural Recruitment Order andClinical Effect,” which is expressly incorporated herein by reference.

The IPG 14 further comprises monitoring circuitry 70 for monitoring thestatus of various nodes or other points 72 throughout the IPG 14, e.g.,power supply voltages, temperature, battery voltage, and the like. Themonitoring circuitry 70 is also configured for measuring electricalparameter data (e.g., electrode impedance and/or electrode fieldpotential). The IPG 14 further comprises processing circuitry in theform of a microcontroller (μC) 74 that controls the control logic 62over data bus 76, and obtains status data from the monitoring circuitry70 via data bus 78. The IPG 14 further comprises memory 80 andoscillator and clock circuit 82 coupled to the μC 74. The μC 74, incombination with the memory 80 and oscillator and clock circuit 82, thuscomprise a microprocessor system that carries out a program function inaccordance with a suitable program stored in the memory 80.Alternatively, for some applications, the function provided by themicroprocessor system may be carried out by a suitable state machine.

Thus, the μC 74 generates the necessary control and status signals,which allow the μC 74 to control the operation of the IPG 14 inaccordance with a selected operating program and stimulation parameters.In controlling the operation of the IPG 14, the μC 74 is able toindividually generate stimulus pulses at the electrical terminals 68using the analog output circuitry 60, in combination with the controllogic 62 and timer logic 66, thereby allowing each electrical terminal68 to be paired or grouped with other electrical terminals 68, includingthe monopolar case electrode, to control the polarity, amplitude, rate,pulse width, pulse shape, and channel through which the current stimuluspulses are provided. The μC 74 facilitates the storage of electricalparameter data measured by the monitoring circuitry 70 within memory 80.

The IPG 14 further comprises a receiving coil 84 for receivingprogramming data (e.g., the operating program and/or stimulationparameters) from the external programmer (i.e., the RC 16 or CP 18) inan appropriate modulated carrier signal, and charging, and circuitry 86for demodulating the carrier signal it receives through the receivingcoil 84 to recover the programming data, which programming data is thenstored within the memory 80, or within other memory elements (not shown)distributed throughout the IPG 14.

The IPG 14 further comprises back telemetry circuitry 88 and atransmission coil 90 for sending informational data to the externalprogrammer. The back telemetry features of the IPG 14 also allow itsstatus to be checked. For example, CP 18 initiates a programming sessionwith the IPG 14, the capacity of the battery is telemetered, so that theCP 18 can calculate the estimated time to recharge. Any changes made tothe current stimulus parameters are confirmed through back telemetry,thereby assuring that such changes have been correctly received andimplemented within the implant system. Moreover, upon interrogation bythe CP 18, all programmable settings stored within the IPG 14 may beuploaded to the CP 18.

The IPG 14 further comprises a rechargeable power source 92 and powercircuits 94 for providing the operating power to the IPG 14. Therechargeable power source 92 may, e.g., comprise a lithium-ion orlithium-ion polymer battery or other form of rechargeable power. Therechargeable battery 92 provides an unregulated voltage to the powercircuits 94. The power circuits 94, in turn, generate the variousvoltages 96, some of which are regulated and some of which are not, asneeded by the various circuits located within the IPG 14. Therechargeable power source 92 is recharged using rectified AC power (orDC power converted from AC power through other means, e.g., efficientAC-to-DC converter circuits, also known as “inverter circuits”) receivedby the receiving coil 84.

To recharge the power source 92, the external charger 22 (shown in FIG.1), which generates the AC magnetic field, is placed against, orotherwise adjacent, to the patient's skin over the implanted IPG 14. TheAC magnetic field emitted by the external charger induces AC currents inthe receiving coil 84. The charging and forward telemetry circuitry 86rectifies the AC current to produce DC current, which is used to chargethe power source 92. While the receiving coil 84 is described as beingused for both wirelessly receiving communications (e.g., programming andcontrol data) and charging energy from the external device, it should beappreciated that the receiving coil 84 can be arranged as a dedicatedcharging coil, while another coil, such as the coil 90, can be used forbi-directional telemetry.

Additional details concerning the above-described and other IPGs may befound in U.S. Pat. No. 6,516,227, U.S. Patent Publication No.2003/0139781, and U.S. patent application Ser. No. 11/138,632, entitled“Low Power Loss Current Digital-to-Analog Converter Used in anImplantable Pulse Generator,” which are expressly incorporated herein byreference.

It should be noted that rather than an IPG, the SCS system 10 mayalternatively utilize an implantable receiver-stimulator (not shown)connected to the stimulation leads 12. In this case, the power source,e.g., a battery, for powering the implanted receiver, as well as controlcircuitry to command the receiver-stimulator, will be contained in anexternal controller inductively coupled to the receiver-stimulator viaan electromagnetic link. Data/power signals are transcutaneously coupledfrom a cable-connected transmission coil placed over the implantedreceiver-stimulator. The implanted receiver-stimulator receives thesignal and generates the stimulation in accordance with the controlsignals.

Referring now to FIG. 5, one exemplary embodiment of an RC 16 will nowbe described. As previously discussed, the RC 16 is capable ofcommunicating with the IPG 14 or CP 18. The RC 16 comprises a casing100, which houses internal componentry (including a printed circuitboard (PCB)), and a lighted display screen 102 and button pad 104carried by the exterior of the casing 100. In the illustratedembodiment, the display screen 102 is a lighted flat panel displayscreen, and the button pad 104 comprises a membrane switch with metaldomes positioned over a flex circuit, and a keypad connector connecteddirectly to a PCB. In an optional embodiment, the display screen 102 hastouchscreen capabilities. The button pad 104 includes a multitude ofbuttons 106, 108, 110, and 112, which allow the IPG 14 to be turned ONand OFF, provide for the adjustment or setting of stimulation parameterswithin the IPG 14, and provide for selection between screens.

In the illustrated embodiment, the button 106 serves as an ON/OFF buttonthat can be actuated to turn the IPG 140N and OFF. The button 108 servesas a select button that allows the RC 16 to switch between screendisplays and/or parameters. The buttons 110 and 112 serve as up/downbuttons that can actuated to increment or decrement any of stimulationparameters of the pulse generated by the IPG 14, including pulseamplitude, pulse width, and pulse rate. For example, the selectionbutton 108 can be actuated to place the RC 16 in an “Pulse AmplitudeAdjustment Mode,” during which the pulse amplitude can be adjusted viathe up/down buttons 110, 112, a “Pulse Width Adjustment Mode,” duringwhich the pulse width can be adjusted via the up/down buttons 110, 112,and a “Pulse Rate Adjustment Mode,” during which the pulse rate can beadjusted via the up/down buttons 110, 112. Optionally, the RC 16 may beplaced in a “Pulse Shaping Adjustment Mode,” which is described infurther detail in U.S. Patent Application Ser. No. 60/951,177, which waspreviously incorporated herein by reference.

Alternatively, dedicated up/down buttons can be provided for eachstimulation parameter. Rather than using up/down buttons, any other typeof actuator, such as a dial, slider bar, or keypad, can be used toincrement or decrement the stimulation parameters. Further details ofthe functionality and internal componentry of the RC 16 are disclosed inU.S. Pat. No. 6,895,280, which has previously been incorporated hereinby reference.

Referring to FIG. 6, the internal components of an exemplary RC 16 willnow be described. The RC 16 generally includes a processor 114 (e.g., amicrocontroller), memory 16 that stores an operating program forexecution by the processor 114, as well as stimulation parameter sets ina look-up table (described below), input/output circuitry, and inparticular, telemetry circuitry 118 for outputting stimulationparameters to the IPG 14 and receiving status information from the IPG14, and input/output circuitry 120 for receiving stimulation controlsignals from the button pad 104 and transmitting status information tothe display screen 102 (shown in FIG. 5). As well as controlling otherfunctions of the RC 16, which will not be described herein for purposesof brevity, the processor 114 generates new stimulation parameter setsin response to the user operation of the button pad 104. These newstimulation parameter sets would then be transmitted to the IPG 14 viathe telemetry circuitry 118. Further details of the functionality andinternal componentry of the RC 16 are disclosed in U.S. Pat. No.6,895,280, which has previously been incorporated herein by reference.

As briefly discussed above, the CP 18 greatly simplifies the programmingof multiple electrode combinations, allowing the physician or clinicianto readily determine the desired stimulation parameters to be programmedinto the IPG 14, as well as the RC 16. Thus, modification of thestimulation parameters in the programmable memory of the IPG 14 afterimplantation is performed by a clinician using the CP 18, which candirectly communicate with the IPG 14 or indirectly communicate with theIPG 14 via the RC 16. That is, the CP 18 can be used by the physician orclinician to modify operating parameters of the electrode array 26 nearthe spinal cord.

As shown in FIG. 3, the overall appearance of the CP 18 is that of alaptop personal computer (PC), and in fact, may be implemented using aPC that has been appropriately configured to include adirectional-programming device and programmed to perform the functionsdescribed herein. Thus, the programming methodologies can be performedby executing software instructions contained within the CP 18.Alternatively, such programming methodologies can be performed usingfirmware or hardware. In any event, the CP 18, under the control of theclinician, may actively control the characteristics of the electricalstimulation generated by the IPG 14 to allow the optimum stimulationparameters to be determined based on patient feedback and forsubsequently programming the IPG 14 with the optimum stimulationparameters.

For example, the clinician may vary stimulation parameters, such as anelectrode combination, which may involve turning on and off electrodes(e.g., turning off electrode E1 as an anode, and turning on electrode E2as an off), or treating the electrode combinations as fractionalizedelectrode combinations, e.g., by gradually shifting current betweenanodic ones of the electrodes 26 and/or gradually shifting currentbetween cathodic ones of the electrodes 26 (e.g., shifting anodicelectrical current from electrode E1 to electrode E2 in 5% increments).Other stimulation parameters, such as the pulse amplitude, pulse width,and pulse rate, may also controlled by the clinician.

To allow the clinician to perform these functions, the CP 18 includes amouse 122, a keyboard 124, and a programming display screen 126 housedin a case 128. It is to be understood that in addition to, or in lieuof, the mouse 122, other directional programming devices may be used,such as a joystick, or directional keys included as part of the keysassociated with the keyboard 124. As shown in FIG. 7, the CP 18generally includes a processor 130 (e.g., a central processor unit(CPU)) and memory 132 that stores a stimulation programming package 134,which can be executed by the processor 130 to allow a clinician toprogram the IPG 14 and RC 16. The CP 18 further includes outputcircuitry 136 (e.g., via the telemetry circuitry of the RC 16) fordownloading stimulation parameters to the IPG 14 and RC 16 and foruploading stimulation parameters already stored in the memory 116 of theRC 16, via the telemetry circuitry 118 of the RC 16.

Further details discussing an exemplary stimulation programming packageis described in U.S. Provisional Patent Application Ser. No. 61/080,187,entitled “System and Method for Converting Tissue Stimulation Programsin a Format Usable by an Electrical Current Steering Navigator,” whichis expressly incorporated herein by reference.

Significant to the present inventions, the CP 18 is designed to avoid,reverse, and/or manage neurological accommodation of the spinal cordfibers.

In one technique that avoids neurological accommodation, the CP 18automatically varies one or more stimulation parameters during aprogramming session. In particular, the clinician varies a firststimulation parameter, and the CP 18 automatically varies a secondstimulation parameter. For example, the clinician may vary the electrodecombination (fractionalized or otherwise) by operating the CP 18 in themanner described above, and the CP 18 may, in addition to varying theelectrode combination in response to clinician control, automaticallyvary a different stimulation parameter (e.g., pulse amplitude, pulsewidth, pulse rate, and polarity).

For the purposes of this specification, a multiphasic pulse (e.g., abiphasic pulse) will be considered a single pulse. For example, a changein polarity of the stimulation energy includes the change of polaritybetween multiphasic pulses, but will not encompass a change in phasewithin a single multiphasic pulse. A change in pulse amplitude of thestimulation energy includes the change of amplitude between multiphasicpulses, but will not encompass the change in amplitude of the phaseswithin a single multiphasic pulse. A change in pulse width of thestimulation energy includes the change of the total width of themultiphasic pulse, but will not encompass the change in width of thephases within a single multiphasic pulse.

The more variance that the stimulation parameter exhibits, the less thechance that neurons will neurologically accommodate to the stimulation.For example, the stimulation parameter may be varied pseudo-randomly(i.e., a process that appears random, but is not, and exhibitsstatistical randomness while being generated by an entirelydeterministic causal process) or randomly. As the stimulation parametersare varied, a plurality of stimulation parameter sets are generated fromthem and transmitted to the IPG 14 via the RC 16, which outputs a pulsedelectrical waveform between the electrodes 12 in accordance with thestimulation parameter sets to stimulate the spinal cord tissue.

As will be described in further detail below, the automatic variance ofthe second stimulation parameter by the CP 18 allows the spinal cordtissue to be stimulated without undergoing neurological accommodationthat would otherwise occur if the second stimulation parameter were notvaried. Based on the result of the spinal cord stimulation (e.g., usingverbal feedback from the patient), the CP 18 can program the IPG 14 viathe RC 16 with a new set of stimulation parameters, which can be storedwithin and subsequently used by the IPG 14 to output pulsed electricalwaveforms to the electrodes 12 in a stand-alone mode (i.e., when notcommunicating with the RC 16 or CP 18). In the alternative case where anexternal controller is used with a receiver-stimulator, the externalcontroller can be programmed with the new set of stimulation parameters,with the receiver-stimulator outputting the pulsed electrical waveformin accordance with this new stimulation parameter set.

As one example, the CP 18 may automatically vary the pulse amplitude ofthe pulsed electrical waveform. As shown in FIG. 8, the amplitudes ofmonophasic pulses may be varied, and as shown in FIG. 9, the amplitudesof biphasic pulses may be varied. In the illustrated embodiment, thepulse amplitudes are varied within a specified amplitude range, with asingle amplitude range being used to limit the anodic pulses of themonophasic pulsed waveform shown in FIG. 8, and two amplitude rangesbeing used to respectively limit the anodic pulses and cathodic pulsesof the biphasic pulsed waveform shown in FIG. 9. To provide the bestresults with respect to preventing neurological accommodation, the pulseamplitudes are preferably varied in a manner that both increases anddecreases the pulse amplitudes, as shown in FIGS. 8 and 9. For example,the pulse amplitudes may be pseudo-randomly or randomly varied.

The CP 18 may also vary the pulse width of the pulsed electricalwaveform, either separately or in addition to varying the pulseamplitude. For example, as shown in FIG. 10, the pulse amplitude andpulse width of each pulse are inversely varied relative to each other(i.e., as the pulse amplitude is increased, the pulse width isdecreased, and as the pulse amplitude is decreased, the pulse width isincreased). Preferably, if both the pulse width and pulse amplitude arevaried, they are varied in such a way as to maintain each pulse within aspecified percentage of the usage range of a strength-duration curve, asshown in FIG. 11.

Notably, a strength-duration curve represents the pulse amplitude andpulse width needed to stimulate a nerve fiber of a specified diameter,and the usage range with respect to the strength-duration curve is thevariance from the strength-duration curve that maintains the stimulationenergy between the point at which it is perceived by the patient and thepoint at which it is uncomfortable for the patient. As one example, thepulse amplitude and pulse width can be varied, so that thestrength-duration of the stimulation energy is maintained within 80% ofthe usage range. Thus, in this case, if the pulse amplitude is varied(either non-randomly, pseudo-randomly, or randomly), the pulse widthrequired to maintain the strength-duration of the stimulation energywithin 80% of the usage range will be computed and used (either in apredetermined manner or dynamically), and if the pulse width is varied(either non-randomly, pseudo-randomly, or randomly), the pulse amplituderequired to maintain the strength-duration of the stimulation energywithin 80% of the usage range will be computed and used (either in apredetermined manner or dynamically).

As another example, the CP 18 may automatically vary the pulse shape ofthe pulsed electrical waveform. Such pulse shapes may include, e.g., asquare pulse, a sinusoidal pulse, exponential pulse, logarithmic pulse,ramped pulse, triangle pulse, trapezoidal pulse, symmetrical biphasicpulse, asymmetrical biphasic pulse, etc. As shown in FIG. 12, the pulseshape of the pulsed electrical waveform is varied by alternating betweena series of square pulses and a series of ramp pulses. Further detailson the use of different pulse shapes are described in U.S. PatentApplication Ser. No. 60/951,177, which was previously incorporatedherein by reference.

As still another example, the CP 18 may automatically burst stimulationon and off, thereby preventing the target nerve fibers from developingneurological accommodation, since the time that the pulsed electricalwaveform is on will only be a percentage of the length of theprogramming session. The burst rate may range anywhere from severaltimes a second to several times an hour. In addition, because patientstend to notice abrupt changes more easily than gradual changes, thebursting of the stimulation will allow the patient to better localizewhere the paresthesia is located and better determine the intensity ofthe paresthesia.

As yet another example, the CP 18 may automatically vary the electrodecombinations, so that the same nerve fibers are not being constantlystimulated. In this case, the CP 18 preferably selects the electrodecombinations in a manner that significantly varies the locus of thestimulation field from one electrode combination to the next electrodecombination. For example, the CP 18 may automatically switch thecathodic current from electrode E1 to electrode E8, then from electrodeE8 to electrode E2, then from electrode E2 to electrode E7, then fromelectrode E7 to electrode E3, then from electrode E3 to electrode E6,then from electrode E6 to electrode E4, and then from electrode E4 toelectrode E5. This should be contrasted with the normal variance ofelectrode combinations, which more gradually varies the locus ofstimulation (e.g., from electrode E1 to electrode E2, than fromelectrode E2 to electrode E3, then from electrode E4 to electrode E5,and so forth), and therefore, is more apt to promote neurologicalaccommodation. If two leads are used, the CP 18 may automatically switchthe cathodic current back and forth between the two leads as well toprovide even more variance of the stimulation loci from one electrodecombination to the next.

Between the automatic switching of electrode combinations, the clinicianmay gradually shift cathodic current (i.e., “steer”) between the presentcathode and the surrounding electrodes or the CP 18 may automaticallyperform this current steering function. Because the clinician may nothave a logical picture of the fractionalized electrode configurationsthat provide the best paresthesia due to the automatic “jumping” of thecathode from one electrode to the next, the CP 18 may generate a map ofwhich electrode combinations (fractionalized or otherwise) had the besteffects on paresthesia.

As an aside, the locus of the stimulation field can be varied (e.g., byvarying the electrode combination or fractionalized electrodecombination) outside of the programming context to prevent neurologicalaccommodation during therapeutic use. In particular, the IPG 14 may beprogrammed to switch back and forth between different electrodecombinations or fractionalized electrode combination) in order todisplace the stimulation field between multiple locations, therebystimulating different bundles of nerve fibers, while maintaining thesame therapeutic effect (e.g., the same physical location on thepatient, such as pain in the lower back, is treated). In this manner,the nerve fibers do not neurologically accommodate to the stimulation.Because the same therapeutic effect is maintained between the differentloci of the stimulation fields, the patient will not readily discernwhen the IPG 14 switches between the different electrode combinations orfractionalized electrode combinations.

The CP 18 may include an optional “Yes” or “No” toggle switch (notshown) that allows the clinician to turn the above-describedneurological accommodation avoidance features on and off. For example,if the clinician anticipates that an IPG for a patient can be programmedin a relatively short period of time, such that neurologicalaccommodation is not likely, the clinician may turn the neurologicalaccommodation avoidance feature off via operation of the toggle switch.In contrast, if the clinician anticipates that an IPG for the patientwill need a relatively long period of time to be programmed, such thatneurological accommodation is likely, the clinician may turn theneurological accommodation avoidance feature on via operation of thetoggle switch.

Oftentimes, neurological accommodation cannot be avoided. However, insome of these cases, neurological accommodation can be reversed. In onetechnique that reverses neurological accommodation, the CP 18, during aprogramming session, prompts the IPG 14 to output a pulsed electricalwaveform between the electrodes 12 while at least one selected electrode12 has a first polarity (e.g., negative polarity), thereby stimulatingthe spinal cord tissue adjacent the selected electrode(s) 12.

When the spinal cord tissue undergoes neurological accommodation inresponse to the pulsed electrical waveform output between the electrodes12 (e.g., based on a predetermined elapsed time), the CP 18 switches theselected electrode(s) 12 from the first polarity to a second polarity(e.g., positive polarity), and prompts the IPG 14 to output the pulsedelectrical waveform between the electrodes 12 while the selectedelectrode(s) 12 have the second polarity, thereby hyperpolarizing thespinal cord tissue (and reversing the neurological accommodation). Forexample, the selected electrode(s) 12 may be operated in the firstpolarity a predetermined number of pulses (e.g., in the range of 10-1000pulses), and then operated in the second polarity a predetermined numberof pulses (e.g., in the range of 10-1000 pulses).

The CP 18 then switches the selected electrode(s) 12 from the secondpolarity back to the first polarity, and prompts the IPG 14 to outputthe pulsed electrical waveform between the electrodes 12 while theselected electrode(s) 12 have the first polarity, thereby stimulatingthe previously hyperpolarized neural tissue (i.e., the neural tissue isdepolarized).

When the selected electrode(s) 12 are in the first polarity, the pulsedelectrical waveform may be output between the electrodes in accordancewith a set of stimulation parameters (e.g., any of those previouslydescribed above), in which case, one or more these stimulationparameters can be varied by the clinician as the pulsed electricalwaveform is output between the electrodes. The IPG 14 may be programmedwith a new set of stimulation parameters based on the result of thespinal cord stimulation.

Preferably, to prevent any undesirable side effects, the amplitude ofthe pulsed electrical waveform output when the selected electrode(s) 12have the first polarity is less than (e.g., one-third) the amplitude ofthe pulsed electrical waveform output when the selected electrode(s) 12have the second polarity. Switching between the polarities may beinitiated either manually by the clinician or automatically by the CP18.

Oftentimes, neurological accommodation can neither be avoided norreversed. In these cases, the CP 18 may manage the effects of theneurological accommodation during the programming process.

In one technique for managing the effects of neurological accommodation,the clinician varies an electrode combination (fractionalized orotherwise) while the pulse rate or pulse width is fixed. For example,the clinician may use the CP 18 to vary the electrode combination, whilethe CP 18 automatically fixes the pulse rate or pulse width. The CP 18then generates a plurality of stimulation parameter sets from thedifferent electrode combinations and the fixed pulse rate or pulsewidth, and prompts the IPG 14 to output a pulsed electrical waveformbetween the electrodes 12 in accordance with these stimulation parametersets, such that paresthesia is achieved while allowing the spinal cordtissue to undergo neurological accommodation.

The CP 18 then automatically changes the pulse rate or pulse width, andthen fixes the changed pulse rate or pulse width while the electrodecombination is varied again by the clinician. The CP 18 then generatesanother plurality of stimulation parameter sets from the differentelectrode combinations and the fixed pulse rate or pulse width, andprompts the IPG 14 to output a pulsed electrical waveform between theelectrodes 12 in accordance with these other stimulation parameter sets,such that the paresthesia is maintained while the spinal cord tissue isstill neurologically accommodated. Notably, without the change in thepulse rate or pulse width, paresthesia may be lost due to theneurological accommodation of the spinal cord tissue. Changing the pulserate may cause the spinal cord tissue to respond differently, becausesome stimulus information is encoded at time between the pulses. Largechanges in pulse rate may be more effective than smaller incrementalchanges in rate over time. Pulse rate has the virtue of affecting theperceived intensity of the stimulation less than other stimulationparameters. Ultimately, the CP 18 may then be operated to program theIPG 14 with a new set of stimulation parameters based on the result ofthe spinal cord stimulation.

The pulse rate or pulse rate can be changed in accordance with apredetermined curve (as shown in FIG. 13), which can be generated, e.g.,based on data collected from patients that have previously undergoneneurological accommodation or on data collected from the currentpatient.

Referring to FIG. 14, if data is to be collected from the currentpatient, the CP 18, at the beginning of the programming session, cangenerate a reference set of stimulation parameters from a firstreference stimulation of the same type as the stimulation parametervaried by the clinician (in this case, a reference electrodecombination) and a second stimulation parameter of the same type as thestimulation parameter changed by the CP 18 (in this case, a referencepulse rate or pulse width) (step 150). Prior to allowing the spinal cordtissue to undergo neurological accommodation (preferably, at thebeginning of the programming process), the CP 18 prompts the IPG 14 tooutput the pulsed electrical waveform between the electrodes 12 inaccordance with the reference stimulation parameter set (in this case, areference electrode combination and a reference pulse rate or pulsewidth), thereby stimulating the spinal cord tissue to provide aparesthesia sensation that can then be remembered by the patient andrecorded (step 152).

Throughout the programming process when various stimulation parametersets (with the currently selected pulse rate or pulse width) are testedby the clinician (step 154), the CP 18 or clinician may thenperiodically return to this reference stimulation parameter set byprompting the IPG 14 to output the pulsed electrical waveform betweenthe electrodes 12 in accordance with the reference stimulation parameterset (step 156). If the spinal cord tissue has undergone neurologicalaccommodation, thereby changing the reference therapeutic effect (inthis case, if the paresthesia sensation is no longer felt or reduced)originally obtained at the beginning of the programming process (step158), the CP 18 determines the pulse rate or pulse width needed to getthe reference paresthesia sensation back by varying the pulse rate orpulse width until the current paresthesia sensation matches thereference paresthesia sensation (using feedback from the patient) (step160). A new reference stimulation parameter set can then be generatedusing this varied pulse rate or pulse width (step 162). This variedpulse rate or pulse width is then used during the programming process(testing various stimulation parameter sets) until the CP 18 (step 154)returns to the new reference stimulation parameter set and a new pulserate or pulse width is determined (step 164). If, at step 158, thespinal cord tissue has not undergone neurological accommodation, therebynot changing the reference therapeutic effect (in this case, theparesthesia sensation feels the same), the pulse rate or pulse width isnot changed, and thus, the current pulse rate or pulse width is usedduring the programming process (testing various stimulation parametersets) until the CP 18 returns to the new reference stimulation parameterset and a new pulse rate or pulse width is determined (step 164).

Ultimately, the CP 18 may then be operated to program the IPG 14 with anew set of stimulation parameters based on the result of the spinal cordstimulation.

In another technique for managing the effects of neurologicalaccommodation during the programming process, the CP 18 prompts the IPG14 to output a pulsed electrical waveform between the electrodes 12 inaccordance with a specified pulse amplitude and a specified pulse width.The CP 18 maintains the pulsed electrical waveform between a firststrength-duration curve for relatively large diameter spinal cord fibersand a second strength-duration curve for relatively small diameterspinal cord fibers, such that the large diameter fibers are stimulatedand the small diameter fibers are not stimulated. For example, as shownin FIG. 15, the pulse amplitude and pulse width can be selected, suchthat the pulsed electrical waveform is maintained at point P1.

The large diameter fibers can then be allowed to neurologicallyaccommodate, and after a predetermine period of time (e.g., 10 minutes),the CP 18 can then automatically increase one or both of the specifiedamplitude and the specified pulse width, such that the pulsed electricalwaveform is on or above the second strength-duration curve, therebystimulating the small diameter fibers. For example, as shown in FIG. 15,the pulse amplitude and pulse width can be selected, such that thepulsed electrical waveform is maintained at point P2. Thus, it can beappreciated that there are least some neurons in the target spinal cordtissue that have not yet neurologically accommodated during thisprocess. Ultimately, the CP 18 may then be operated to program the IPG14 with a new set of stimulation parameters based on the result of thespinal cord stimulation.

In another technique for managing the effects of neurologicalaccommodation, the CP 18, at the beginning of the programming process,prompts the IPG 14 to output a pulsed electrical waveform between theelectrodes 12, such that the spinal cord tissue is stimulated andundergoes neurological accommodation. Preferably, the pulsed electricalwaveform is initially output with the highest pulse amplitude tolerablefor the patient. The CP 18 then decreases the pulse amplitude of thepulsed electrical waveform, generates a plurality of stimulationparameter sets having the decreased amplitude, and again prompts the IPG14 to output the pulsed electrical waveform with the decreased pulseamplitude between the electrodes 12 in accordance with the stimulationparameter sets, such that the neural tissue is stimulated and remainsneurologically accommodated. Ultimately, the CP 18 may then be operatedto program the IPG 14 with a new set of stimulation parameters based onthe result of the spinal cord stimulation.

It should be appreciated that because the targeted areas of the spinalcord tissue are neurologically accommodated throughout the entireprogramming process (i.e., the targeted areas are preconditioned to beneurologically accommodated), the sensation of paresthesia achievedduring the neurological accommodation is not lost during the programmingprocess.

Although particular embodiments of the present inventions have beenshown and described, it will be understood that it is not intended tolimit the present inventions to the preferred embodiments, and it willbe obvious to those skilled in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe present inventions. Thus, the present inventions are intended tocover alternatives, modifications, and equivalents, which may beincluded within the spirit and scope of the present inventions asdefined by the claims.

1. A method of operating a neurostimulation device, comprising: varyinga first stimulation parameter under user control while fixing a secondstimulation parameter; generating a plurality of stimulation parametersets from the varied first stimulation parameter and the fixed secondstimulation parameter; outputting a pulsed electrical waveform from theneurostimulation device between a plurality of electrodes in accordancewith the plurality of stimulation parameter sets, such that atherapeutic effect is achieved while allowing neural tissue to undergoneurological accommodation; changing the second stimulation parameter;varying the first stimulation parameter under user control while fixingthe second changed stimulation parameter; generating another pluralityof stimulation parameter sets from the varied first stimulationparameter and the fixed changed second stimulation parameter; outputtingthe pulsed electrical waveform from the neurostimulation device betweenthe plurality of electrodes in accordance with the other plurality ofstimulation parameter sets to maintain the therapeutic effect while theneural tissue is neurologically accommodated.
 2. The method of claim 1,further comprising programming the neurostimulation device with a newset of stimulation parameters based on a result of the therapeuticeffect.
 3. The method of claim 1, wherein the first stimulationparameter is an electrode combination.
 4. The method of claim 1, whereinthe first stimulation parameter is a fractionalized electrodecombination.
 5. The method of claim 4, wherein the fractionalizedelectrode combination is varied by gradually shifting current betweenanodic ones of the electrodes or gradually shifting current betweencathodic ones of the electrodes.
 6. The method of claim 1, wherein thesecond stimulation parameter is automatically changed.
 7. The method ofclaim 1, wherein the second stimulation parameter is a pulse rate. 8.The method of claim 1, wherein the second stimulation parameter is apulse width.
 9. The method of claim 1, wherein the second stimulationparameter is changed in accordance with a predetermined curve.
 10. Themethod of claim 9, further comprising generating the predetermined curvebased on data collected from patients that have undergone neurologicalaccommodation.
 11. The method of claim 9, further comprising: generatinga reference set of stimulation parameters from a first referencestimulation parameter of the same type as the first stimulationparameter, and a second stimulation parameter of the same type as thesecond stimulation parameter; prior to allowing the neural tissue toundergo neurological accommodation, outputting the pulsed electricalwaveform from the neurostimulation device between the electrodes inaccordance with the reference stimulation parameter set, therebystimulating the neural tissue to provide a reference therapeutic effect;and after allowing the neural tissue to undergo neurologicalaccommodation, outputting the pulsed electrical waveform from theneurostimulation device between the electrodes in accordance with thereference stimulation parameter set, thereby providing an effectdifferent from the reference therapeutic effect, and varying the secondreference stimulation parameter until the effect matches the referencetherapeutic effect, wherein the varied second reference stimulationparameter is used as the changed second stimulation parameter.
 12. Themethod of claim 1, wherein the neural tissue is spinal cord tissue, andthe therapeutic effect is pain relief.
 13. A method of operating aneurostimulation device, comprising: outputting a pulsed electricalwaveform from the neurostimulation device between a plurality ofelectrodes in accordance with a specified pulse amplitude and aspecified pulse width; maintaining the pulsed electrical waveformbetween a first strength-duration curve for relatively large fibers ofneural tissue and a second strength-duration curve for relatively smallfibers of the neural tissue, whereby the relatively large fibers arestimulated and the relatively small fibers are not stimulated; allowingthe relatively large fibers of the neural tissue to neurologicalaccommodate when the pulsed electrical waveform is between the first andsecond strength-duration curves; and increasing one or both of thespecified amplitude and the specified pulse width, such that the pulsedelectrical waveform is on or above the second strength-duration curve,whereby the relatively small fibers are stimulated.
 14. The method ofclaim 13, further comprising programming the neurostimulation devicewith a new set of stimulation parameters based on a result of the neuralstimulation.
 15. The method of claim 13, wherein the specified amplitudeis increased.
 16. The method of claim 13, wherein the specified pulsewidth is increased.
 17. The method of claim 13, wherein the one or bothof the specified amplitude and the specified pulse width isautomatically increased.
 18. The method of claim 13, wherein the one orboth of the specified amplitude and the specified pulse width isincreased at a predetermined period of time after the pulsed electricalwaveform is initially output by the neurostimulation device.
 19. Themethod of claim 13, wherein the neural tissue is spinal cord tissue. 20.The method of claim 13, further comprising varying a stimulationparameter under user control.
 21. The method of claim 20, wherein thestimulation parameter is an electrode combination.
 22. The method ofclaim 20, wherein the first stimulation parameter is a fractionalizedelectrode combination.
 23. The method of claim 22, wherein thefractionalized electrode combination is varied by gradually shiftingcurrent between anodic ones of the electrodes or gradually shiftingcurrent between cathodic ones of the electrodes.
 24. A method ofprogramming a neurostimulation device, comprising: initially outputtinga pulsed electrical waveform from the neurostimulation device between aplurality of electrodes, such that neural tissue of a patient isstimulated and undergoes neurological accommodation; decreasing a pulseamplitude of the pulsed electrical waveform; generating a plurality ofstimulation parameter sets having the decreased amplitude; outputtingthe pulsed electrical waveform with the decreased pulse amplitude inaccordance with the stimulation parameter sets, such that the neuraltissue is stimulated and remains neurologically accommodated; andprogramming the neurostimulation device with a new set of stimulationparameters based on a result of the neural tissue stimulation.
 25. Themethod of claim 24, wherein the pulsed electrical waveform is initiallyoutput with the highest pulse amplitude tolerable for the patient. 26.The method of claim 24, wherein the neural tissue is spinal cord tissue.27. The method of claim 24, further comprising varying a stimulationparameter under user control, wherein the plurality of stimulationparameter sets are generated from the varied stimulation parameter. 28.The method of claim 24, wherein the stimulation parameter is anelectrode combination.
 29. The method of claim 24, wherein the firststimulation parameter is a fractionalized electrode combination.
 30. Themethod of claim 29, wherein the fractionalized electrode combination isvaried by gradually shifting current between anodic ones of theelectrodes or gradually shifting current between cathodic ones of theelectrodes.